1. Field of the Invention
This invention relates to key switch assemblies of the type used for calculators and telephones and more particularly to such assemblies having a dual spring actuation mechanism.
2. Discussion of the Prior Art
A keyboard frequently represents a major portion of the cost of a product such as a calculator or a pushbutton telephone. It thus becomes extremely important to minimize keyboard costs while maintaining a satisfactory tactile impression for the keyboard operator. Great effort has thus been made to develop less expensive batch fabricated keyboards with better tactile feel and longer lifetime. While significant improvements have resulted from this development effort, further improvement is needed because of the large production volumes of keyboard assemblies and because of the significant cost contributions which they make to many products.
One arrangement of a batch fabricated switch assembly is illustrated in U.S. Pat. No. 3,383,487 to Weiner. Weiner teaches the use of opposed, mating oppositely directed protrusions with switch closure contacts on the inside thereof. While this arrangement meets the requirements of an inexpensive, batch fabricated switch assembly, it does not provide the elegance of an actuator key nor permit selection of desired tactile impression for an operator.
Another keyboard arrangement in which actuator keys drive individual diaphragms is taught by Boulanger in U.S. Pat. No. 3,783,205. This arrangement has individual actuator keys but does not have the advantages of a low cost batch fabricated switch assembly nor a dual spring actuator as taught by the present invention.
Double spring key actuators are described in U.S. Pat. No. 3,993,884 to Kondur et al, U.S. Pat. No. 3,780,237 to Seeger, Jr. et al, and U.S. Pat. No. 3,856,998 to Sims, Jr. These patents teach arrangements which are relatively complex and expensive and do not teach the advantages of combining a dome shaped switch closure assembly with a dual spring actuator assembly.